JS: move expressions test to box tests

js/js.translator/testData/box/expression/cast/castExtensionToKMutableProperty.kt

@@ -0,0 +1,21 @@
+package foo
+
+import kotlin.reflect.KProperty1
+import kotlin.reflect.KMutableProperty1
+
+class A
+
+var A.x: Int
+    get() = 23
+    set(value) { }
+
+fun box(): String {
+    assertEquals(true, (A::x as Any) is KProperty1<*, *>)
+    assertEquals(true, (A::x as Any) is KMutableProperty1<*, *>)
+    assertEquals(23, ((A::x as Any) as KProperty1<A, Any>)(A()))
+    assertEquals(23, ((A::x as Any) as KMutableProperty1<A, Any>)(A()))
+    assertEquals(false, (23 as Any) is KMutableProperty1<*, *>)
+    assertEquals(false, ({ A().x } as Any) is KMutableProperty1<*, *>)
+
+    return "OK"
+}